Numerical analysis and experiment of internal flow characteristic in a cross flow fan with different diameter blades

A blade-twisted Cross-Flow-Fan (CFF) has lower noise and better tone than a straight cross flow fan. However, the price and the manufacture cost of a blade-twisted CFF are higher than that of a straight cross flow fan. In order to decrease the noise of the straight CFF and replace the blade-twisted CFF, a cross flow fan with a large diameter blade are distributed either ahead of or behind a small diameter blade is designed. The blades are also unequally distributed along the circumference. In addition, the numerical analysis and experimental research are carried out to study the internal flow characteristic in a newly designed CFF. The numerical analysis is based on unsteady Navier-Stokes equations and moving mesh technique. The numerical results show that, the eccentric vortex core of the CFF is located at the tangential line between the rotational center and the tongue of the casing. The eccentric vortex core is located near the inner circumference of the impeller. It moves within the inner area of a 2-mm diameter circle when the fan rotates unsteadily. The large and small blades change the clearance length between the impeller and the tongue of the casing when the impeller rotates. It decreases the blade passing-by-frequency noise and improves the rotating tone. The newly designed cross flow fan with different diameter blades decreases the aerodynamic noise of the fan, and it can achieve the noise decreasing effect of blade-twisted cross flow fan.